Location: Insect Control and Cotton Disease Research
2017 Annual Report
Objectives
Objective 1: Develop novel detection technologies for the stink bug complex, Lepidoptera, boll weevil, and their associated host plants. (NP304, Component 3, Problem Statement 3A1 and Problem Statement 3B1).
Subobjective 1A: Enhance airborne remote sensing techniques to detect host plants.
Subobjective 1B: Improve attraction and increase duration of attractiveness of insect pheromone lures.
Subobjective 1C: Improve detection of pest insect populations in response to climate change.
Objective 2: Develop knowledge of insect-pathogen interactions and critical life functions of piercing-sucking insects to regulate and disrupt these processes. (NP304,
Component 3, Problem Statement 3A2 and Problem Statement 3B2).
Subobjective 2A: Identify hemipterans that act as pathogen reservoirs and assess potential for transmission of pathogens.
Subobjective 2B: Determine the propensity for individual infected insects to inoculate multiple bolls.
Subobjective 2C: Ascertain the retention time of pathogenic organisms within the digestive tract of hemipterans.
Objective 3: Develop pest management strategies and delivery systems, such as neuropeptide mimic-based systems, that disrupt critical life processes of insects including stink bugs, Lepidoptera, and boll weevils. (NP304, Component 3, Problem Statement 3A2 and Problem Statement 3B2).
Subobjective 3A: Identify native NP and determine their role in regulating critical life processes in stink bugs, Lepidoptera, Lygus, and boll weevils.
Subobjective 3B: Develop biostable, bioavailable mimics of regulatory NP that disrupt critical life processes of stink bugs, boll weevils, bollworms, and budworms.
Subobjective 3C: Exploit secondary metabolites of cotton plants to reduce insect pest abundance and feeding damage.
Approach
Ecologically based management of field crop pests is critical for sustaining agricultural productivity/health and for reducing costs and minimizing undesirable environmental consequences associated with reliance on chemical pesticides. This project focuses on development of pest trapping/monitoring systems to detect host plant distributions, pest abundance, pest dispersal, pest transmission of plant pathogens, and exploitation of host plant defense mechanisms and neuropeptide mimics that disrupt critical life processes of insect pests. Project objectives will be accomplished through three main research areas that lead to development of: 1) technologies that detect pests and pest habitats, and models that simulate response of pest migration to climate change; 2) methods to understand the biology and ecology of plant pathogen vectoring by stink bugs and other piercing-sucking insect pests; and 3) novel pest management technologies and strategies such as neuropeptide (NP) mimics and exploitation of host plant defense traits. Results of project research are expected to provide producers and crop consultants with the appropriate scientific knowledge and technologies to make effective pest management decisions with minimal environmental impact. This project combines entomological, biochemical, and meteorological expertise to create a research program that defines how pests utilize host plants, disperse, and infest and infect target crops, and how pest activity can be altered by the use of neuropeptide mimics and natural plant defense traits to achieve environmentally safe crop protection.
Progress Report
Work under this project in FY 2017 resulted in significant progress in monitoring the landscape distribution and physiological condition of cotton insect pest populations, describing the presence and abundance of pest species relative to host crops, and developing novel biologically based pest management technologies. In work addressing Objective 1, individual volunteer cotton plants were identified within mixed vegetation by analysis of airborne multispectral reflectance images acquired by a multi-channel camera, and associated technology transfer to an industry partner is underway with support from the ARS Innovation Fund. Advanced genetic sequencing techniques and other population genomic tools are being used to develop genetic markers from which to infer the geographical association of boll weevils, and to distinguish boll weevils from other closely related weevil species. These genomic tools are also being used to investigate the spatial scale of cotton fleahopper movement from weed hosts into cotton fields, and to determine the level of intermixing among fleahopper populations in weed hosts and cotton. Project work is monitoring insect migratory flight activity using a vertical-looking radar from which to develop operational weather radar algorithms that estimate long-distance pest migration. An atmospheric transport model and a population ecology model have been coupled to simulate migration of sugarcane aphids as part of the ARS Sugarcane Aphid Areawide Pest Management Project. In work addressing Objective 2, adult and newly hatched stink bug nymphs were discovered to ingest and retain plant disease pathogens in their feeding apparatus (stylets) after acquisition from an infected food source. Greenhouse studies indicated that adults which subsequently fed upon cotton bolls introduced the disease-causing pathogens into bolls. In work addressing Objective 3, laboratory feeding bioassays using cotton plants in which the gossypol pathway had been blocked conclusively confirmed the importance of the natural compounds gossypol, heliocides, and hemigossypolone as feeding deterrents for bollworm larvae. Efforts are now underway to target this gene to increase production of these natural plant compounds to enhance cotton resistance to insect pests. Neuropeptides of several classes were identified from the central nervous system of the boll weevil. In addition, the work mapped neuropeptide storage and release sites and characterized the structures of seven distinct peptide hormones in the nervous system of this insect pest. The studies identified a hormone in the boll weevil that has a unique structure, which could allow for the development of stable versions that can act as control agents specific to this insect. This information will aid in determining the functional roles of these different classes of neuropeptides in boll weevils and other related insect pests, which may lead to development of practical neuropeptide-like substances that can effectively and specifically control pest insects in an environmentally-friendly fashion.
Accomplishments
1. New avenue for novel mosquito repellents discovered. Mosquitoes are responsible for spreading such diseases as yellow fever, zika, and chikungunya to humans. Development of new, environmentally-friendly repellents is a high priority, particularly for the protection of U.S. troops deployed overseas in areas where these diseases are readily spread. ARS researchers at College Station, Texas, along with collaborators at Texas A&M University and the University of Paris-Saclay, identified a class of ‘neuropeptide’ hormone that is involved in the process of taste perception in the legs and mouth parts of mosquitoes. A novel version of a neuropeptide of the ‘Insect Kinin’ class was subsequently developed that deters and/or repels mosquitoes from feeding, causing them to show an immediate ‘fly-away’, ‘walk-away’ and/or ‘jump-away’ behavior. This aversive behavior was shown to be mediated by the active site of the neuropeptide hormone. The work, sponsored by a joint USDA/DoD program and published in the Proceedings of the National Academy of Sciences USA, represents a major breakthrough in the development of a completely new, practical, and environmentally friendly strategy based on neuropeptide-like substances that can act as repellents to mosquitoes that spread debilitating disease in humans and animals.
2. Airborne identification of potential boll weevil habitats. Boll weevil eradication progress in South Texas has been hindered by the subtropical climate which supports year-round growth of cotton. Regrowth of plants following harvest, and plants arising from unharvested seed, support reproduction and sustain weevils beyond the production season. Thus, timely detection/elimination of such plants is critical for eradication success. ARS researchers at College Station, Texas, developed a technique to analyze high-altitude images for remote identification of cotton plants that may harbor weevils. This technique is currently being evaluated by the Texas Boll Weevil Eradication Foundation to identify cotton fields as well as volunteer and regrowth plants in the Texas Winter Garden crop production area, which has recently been re-infested with boll weevils.
3. Gene identified that regulates cotton plant resistance to insects. Resistance of glanded cotton plants to insect pests has been mainly attributed to the presence of terpenoids (e.g., gossypol) in the glands, which also contain other essential oils. ARS researchers at College Station, Texas, identified a gene (cytochrome P450) that regulates synthesis of these terpenoids. Reduced expression of this gene via a molecular technique known as RNAi resulted in a 90% reduction in overall levels of these terpenoids in leaves without reducing the number of glands or levels of other terpene volatiles. Bollworm larvae fed leaves or fruit from these RNAi cotton plants weighed significantly more than those fed leaves or fruit from their respective wild-type cotton plants, suggesting larvae fed more readily on the RNAi cotton plants. Although this effect would be counterproductive from a pest management standpoint, the results unequivocally demonstrate the importance of these terpenoids in insect resistance. Efforts are underway to increase expression of this gene in plants to potentially increase terpenoid production in glands and, subsequently, enhance cotton resistance to insects.
4. Southern green stink bugs transmit disease-causing pathogens of cotton. Stink bugs and coincidental occurrences of boll rot in cotton have become more prevalent following successes by boll weevil eradication programs. However, information is lacking on the association between stink bugs and the increase in boll rot, and on the insect’s potential to breach the boll wall with the feeding apparatus (stylets). ARS researchers at College Station, Texas, demonstrated the potential of southern green stink bug adults and immatures (first instars) to ingest pathogens from a food source containing the disease-causing pathogen of cotton, and developed a mathematical model to calculate stylet penetration estimates for adult and nymphal southern green stink bugs and other sucking insect pests. Stylet penetration estimates indicate that cotton bolls are susceptible to breaching of the carpel wall from the first day of boll set throughout the growing season. Although stink bugs are usually identified as late-season pests, these findings established that the bolls are susceptible at boll set, and management tactics (e.g., insecticide applications) may need to be adjusted accordingly to address the population of pest species that may be feeding on younger bolls earlier in the production season.
Review Publications
Knutson, A., Suh, C.P. 2016. The role of replaceable and density-dependent mortality in assessing augmentative releases of Trichogramma in U.S. cotton. In: Vinson, S.B, Greenberg, S.M., Liu, T.-X., Rao, A., Volosciuk, L.F., editors. Biological Control of Pests Using Trichogramma: Current Status and Perspectives. China: Northwest A&F University Press. p.394-404.
Suh, C.P., Spurgeon, D.W. 2016. Boll weevils (Coleoptera: Curculionidae) continue to release pheromone following host removal. Journal of Entomological Science. 51(4):332-335.
Yang, C., Suh, C.P., Westbrook, J.K. 2017. Early identification of cotton fields using mosaicked aerial multispectral imagery. Journal of Applied Remote Sensing (JARS). 11(1):016008.
Nagoshi, R.N., Fleischer, S., Meagher Jr, R.L., Hay-Roe, M., Khan, A., Murua, M.G., Silvie, P., Westbrook, J.K. 2017. Fall armyworm migration across the Lesser Antilles and the potential for genetic exchanges between North and South American populations. PLoS One. 12(2):e0171743.
Kwan, H., Agha, M.A., Smith, R.C., Nachman, R.J., Marion-Poll, F., Petrantonio, P.V. 2016. A leucokinin mimic elicits aversive behavior in mosquito Aedes aegypti (L.) and inhibits the sugar taste neuron. Proceedings of the National Academy of Sciences USA. 113(25):6880-6885.
Esquivel, J.F. 2016. Nezara viridula (L.) in Central Texas: II. Seasonal occurrence of black spotted condition in adult females. Southwestern Entomologist. 41:905-912.
Wagner, T., Suh, C.P., Liu, J., Puckhaber, L.S. 2017. Increased Helicoverpa zea (Boddie) larval feeding on cotton plants with RNAi construct CYP82D109 that blocks gossypol-related terpenoid synthesis. Southwestern Entomologist. 42:287-290.
